1. Field of the Invention
The present invention relates to a method for manufacturing substrates for depositing diamond thin films.
2. Related Art
Diamond thin films are utilized for protection films of semiconductor chips and coating films for various cutting tools.
To deposit diamond thin films as carbonaceous thin films so as to have a reasonable crystal structure, it is necessary to consider not only growing methods therefor but also materials of substrates on which diamond thin films are deposited.
Conventionally, there have been used single crystal diamond substrates since they are composited by the same material as that of the growth films to be deposited. When they are used, it is possible to obtain thin films with an excellent crystal structure. Such a method as mentioned above is called homo-epitaxial growth method.
On the other hand, there has been known the hetero-epitaxial growth method in which films are grown on substrates made of a material different from that of the films. This method enables application of diamond thin films for a variety of technical fields since various substrates are available.
At present, a variety of materials such as silicon, silicon carbide and the like are used for this method.
It has been also tried to process the surface of the substrate artificially together with selection of materials therefor. For instance, roughing of the surface of the silicon substrate using an inert ion beam or diamond grinding stone has been proposed.
In order to form diamond thin films according to the homo-epitaxial method, it becomes necessary to use single crystal diamond substrates. However, the diamond substrate is very expensive and it is difficult to make diamond substrates of large scale.
On the other hand, the selection of the substrate is important in order to form carbonaceous thin films according to the hetero-epitaxial method.
The generation and growth of diamond kernels in the initial phase of the deposition of films are important for the growth of diamond films and it depends on the material and the state of surface of the substrate to be used.
Conventionally, the artificial roughing of the surface of the substrate has been proposed to increase the generation density of diamond kernels. However, in this method, it is impossible to control the crystal orientation of the film to be deposited although the generation density of diamond kernels is increased.
In general, the hetero-epitaxial method is inferior to the homo-epitaxial method on the crystalline structure of the film.
As mentioned above, conventional substrates used for depositing diamond thin films are not so satisfactory to obtain diamond thin films with an excellent crystal structure. Especially in the hetero-epitaxial method, there have been known no effective improvements in controlling the crystal structure and orientation of the diamond thin film.